title: Mild oxidative stress induces S-glutathionylation of STAT3 and enhances chemosensitivity of tumoural cells to chemotherapeutic drugs.
abstract: STAT3 is a transcription factor constitutively activated in a variety of cancers that has a critical role in the inhibition of apoptosis and induction of chemoresistance. Inhibition of the STAT3 signaling pathway suppresses cell survival signals and leads to apoptosis in cancer cells, suggesting that direct inhibition of STAT3 function is a viable therapeutic approach. Herein, we identify the naturally occurring sesquiterpene lactone cynaropicrin as a potent inhibitor of both IL-6-inducible and constitutive STAT3 activation (IC50=12 μM). Cynaropicrin, which contains an α-β-unsaturated carbonyl moiety and acts as potent Michael reaction acceptor, induces a rapid drop in intracellular glutathione (GSH) concentration, thereby triggering S-glutathionylation of STAT3. Furthermore, glutathione ethylene ester, the cell permeable form of GSH, reverts the inhibitory action of cynaropicrin on STAT3 tyrosine phosphorylation. These findings suggest that this sesquiterpene lactone is able to induce redox-dependent post-translational modification of cysteine residues of STAT3 protein to regulate its function. STAT3 inhibition led to the suppression of two anti-apoptotic genes, Bcl-2 and survivin, in DU145 cells that constitutively express active STAT3. This event may be responsible for the decline in cell viability after cynaropicrin treatment. As revealed by PI/annexin-V staining, PARP cleavage, and DNA ladder formation, cynaropicrin cytotoxicity is mediated by apoptosis. Finally, cynaropicrin displayed a slight to strong synergism with two well-established chemotherapeutic drugs, cisplatin and docetaxel. Taken together our studies suggest that cynaropicrin suppresses the STAT3 pathway, leading to the down-regulation of STAT3-dependent gene expression and chemosensitization of tumour cells to chemotherapy.
authors.affiliation: Department of Life and Reproduction Sciences, Biochemistry Section, University of Verona, 37134 Verona, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Butturini
authors.affiliation: Department of Life and Reproduction Sciences, Biochemistry Section, University of Verona, 37134 Verona, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Carcereri de Prati
authors.affiliation: Department of Life and Reproduction Sciences, Biochemistry Section, University of Verona, 37134 Verona, Italy.
authors.forename: Giulia
authors.initials: G
authors.lastname: Chiavegato
authors.affiliation: Department of Medicine, University of Verona, 37134 Verona, Italy.
authors.forename: Antonella
authors.initials: A
authors.lastname: Rigo
authors.affiliation: Department of Life and Reproduction Sciences, Biochemistry Section, University of Verona, 37134 Verona, Italy.
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Cavalieri
authors.affiliation: Department of Life and Reproduction Sciences, Biochemistry Section, University of Verona, 37134 Verona, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Darra
authors.affiliation: Department of Life and Reproduction Sciences, Biochemistry Section, University of Verona, 37134 Verona, Italy. Electronic address: sofia.mariotto@univr.it.
authors.forename: Sofia
authors.initials: S
authors.lastname: Mariotto
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects*; D002945:Cisplatin / Q000494:pharmacology; D003603:Cytotoxins / Q000494:pharmacology*; D000077143:Docetaxel; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D005978:Glutathione / Q000031:analogs & derivatives / Q000032:analysis / Q000378:metabolism; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins / Q000037:antagonists & inhibitors; D007783:Lactones / Q000494:pharmacology*; D018384:Oxidative Stress; D010766:Phosphorylation / Q000187:drug effects; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors; D017382:Reactive Oxygen Species / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000037:antagonists & inhibitors* / Q000737:chemistry; D012717:Sesquiterpenes / Q000494:pharmacology*; D015398:Signal Transduction; D000077022:Survivin; D043823:Taxoids / Q000494:pharmacology
chemical_list: D000970:Antineoplastic Agents; C107489:BIRC5 protein, human; D003603:Cytotoxins; D051034:Inhibitor of Apoptosis Proteins; D007783:Lactones; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D012717:Sesquiterpenes; D000077022:Survivin; D043823:Taxoids; D000077143:Docetaxel; C042431:S-ethyl glutathione; D011065:Poly(ADP-ribose) Polymerases; D005978:Glutathione; C075687:cynaropicrin; D002945:Cisplatin
keywords: 5,5′-dithiobis(2-nitrobenzoic acid); Apoptosis; Chemosensitivity; DTNB; Free radicals; GEE; GSH; GSSG; ROS; S-glutathionylation; STAT3; Sesquiterpenes; glutathione; glutathione disulfide; glutathione ethylene ester; reactive oxygen species; signal transducer and activator of transcription 3